MK2 cables work fine, but you may need to mount the callipers upside down/left to right if they are pre-88, not sure about post 88.
Don't bother changing the rear discs, the standard kit is fine - the rear brakes are *barely* used.
Freeing it off is either a case of stripping of the calliper and winding it back and forth to free up the piston, or removing the seals, cleaning and replacing (arse of a job).